Internet advertising firms are losing hundreds of millions of dollars following the introduction of a new privacy feature from Apple that prevents users from being tracked around the web.

Advertising technology firm Criteo, one of the largest in the industry, says that the Intelligent Tracking Prevention (ITP) feature for Safari, which holds 15% of the global browser market, is likely to cut its 2018 revenue by more than a fifth compared to projections made before ITP was announced.

With annual revenue in 2016 topping $730m, the overall cost of the privacy feature on just one company is likely to be in the hundreds of millions of dollars.

Dennis Buchheim, general manager of the Interactive Advertising Bureau’s Tech Lab, said that the feature would impact the industry widely.

“We expect a range of companies are facing similar negative impacts from Apple’s Safari tracking changes. Moreover, we anticipate that Apple will retain ITP and evolve it over time as they see fit,” Buchheim said.